In U.S. Pat. No. 4,387,339 a method and apparatus are disclosed for indicating the width of the gap between the refiner discs in a refiner by means of reluctance measurement. The object of this approach is to prevent metallic contact between the refiner discs. A transmitter is defined in detail in this patent, and is disclosed as being inserted in the surface of one of the refiner discs (the stationary disc).
In order to achieve optimum measurement in such a device, the transmitter is formed as an integral part of the surface of the refiner disc, and in that manner the transmitter is worn in a similar manner to that of the beating surface. Therefore, the real distance between the refiner discs is indicated at all times. In order to function, the transmitter requires a current supply. Furthermore, the results of these measurements must be transferred from the transmitter to a receiver.
The aforesaid arrangement can be easily applied to refiners which include only one disc which rotates and a second disc which is stationary. The transmitter can then be placed on the stationary disc, and no problems then arise with respect to either the current supply or utilization of the measurement signals. In a refiner comprising two counter-rotating refiner discs, however, problems arise with the transfer of the electrical supply and of the measurement signals between the transmitter on the rotary disc and the stationary parts of the refiner.